Hitherto, studies of various Si-based elements using a porous film have been made. A plurality of holes are formed inside the porous film, and the porous film may function as a low dielectric constant film (sometimes referred to as a low-k film) due to the plurality of holes. In a case where the porous film is processed through etching, a fluorocarbon-based gas is generally used. However, a technique using SiF4 gas has also been studied (Non Patent Literature 1: “New fluorocarbon free chemistry proposed as solution to limit porous SiOCH film modification during etching”, N. Posseme, et al., IITC 2013, LET/AMAT, and Non Patent Literature 2: “Plasma Etch Challenges at 14 nm and Beyond Technology Nodes in the BEOL”, Ph. Brun, et al., IITC 2015 3-1 ST Micro/Leti). In a case of etching using SiF4 gas, a Si (silicon)-based film is formed on the surface of the porous film as a protective film. In addition, for the protective film, a technique regarding a film containing Ge (germanium) as well as the Si-based film described above has been developed (Patent Literature 1: Japanese Patent Application Laid-Open Publication No. H8-203847, and Patent Literature 2: Japanese Patent Application Laid-Open Publication No. 2013-225604).